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Science (086) — CBSE Class 10 board question

Q1. [1] § 1.2.3 Displacement Reaction
Assertion (A) : The colour of aqueous solution of copper sulphate turns colourless when a piece of lead is added to it. Reason (R) : Lead is more reactive than copper, and hence displaces copper from its salt solution.
  1. (a) Both (A) and (R) are true and (R) is the correct explanation of (A).
  2. (b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
  3. (c) (A) is true, but (R) is false.
  4. (d) (A) is false, but (R) is true.
Previously asked in CBSE board exam
2023 31/1/1 Q17
Generated by claude-sonnet-4-6 · 2026-06-14 10:27 · grounding rag
Model Answer

(a) Both (A) and (R) are true and (R) is the correct explanation of (A).

Lead is more reactive than copper and displaces copper from copper sulphate solution, turning the blue solution colourless: Pb + CuSO₄ → PbSO₄ + Cu.

Explanation

The textbook (equation 1.26) shows Pb displacing Cu from CuCl₂; it also states "Zinc and lead are more reactive than copper." The same logic applies to CuSO₄ — lead displaces copper, removing the Cu²⁺ ions responsible for the blue colour, making the solution colourless. So both A and R are true, and R correctly explains A. Option (a) is correct.

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